The present invention is directed toward new transition metal compounds containing bidentate E-phenoxide ligands and formal neutral ligands that are useful for the oligomerization and polymerization of olefins. Bidentate E-phenoxide ligands form 6-membered metallacycle rings when bound to a transition metal. These compounds, and optionally an activator, can be used to oligomerize or polymerize unsaturated monomers such as olefins.
Other polymerization catalysts employing bidentate ligands based on phenoxides that form six-membered metallacycle rings have been reported in the art. Mitsui has reported low activity transition metal complexes containing azo-phenoxide ligands (European Patent EP-A1 0 990 664). Low activity, low molecular weight catalysts that use an azo-phenoxide ligand based upon a naphthyl ring have also been reported in the literature (Macromolecules, 2002, 35, 6071). Catalysts based upon keto-amide structures have been reported by DuPont (WO 98/30609). These show poor activity and low molecular weight or poor molecular weight control. Imine-phenoxide catalysts based on nickel have been reported both by Grubbs (Science 2000, 287, 460; Organometallics 1998, 17, 3149; J. Polym. Sci. A. 2002, 40, 2842; WO 98/42665; WO 2000/56786; WO 2000/56787; WO 2000/56781) and DuPont researchers (WO 98/30609). These imine-phenoxide systems were examined alongside the azo-phenoxide catalysts reported here and the imine-phenoxide systems were shown to give lower molecular weight polymer.
Other references of interest include: WO 98/42664; Hicks, F.; Brookhart, M. Organometallics 2001, 20, 3217; Laali, K.; Szele, I.; Zollinger, H., Helvetica Chimica Acta 1983, 66, 1737; and Petrillo, G.; Novi, M.; Garbarino, G.; Filiberti, M., Tetrahedron 1989, 45, 7411.
Functionalized polyolefins are of interest for many industrial applications due to the polymer property enhancements bestowed by polar groups. These advantages can include improved impact strength, adhesion, dyeability, printability, solvent resistance, melt strength, miscibility with other polymers, and gas barrier properties, as compared to unfunctionalized polyolefins.
ExxonMobil currently sells ester-(Optema™, Enable™), acetate-(Escorene™), and acid/ionomer-functionalized polyethylenes (Escor™, Iotek™) made by free-radical processes for adhesive, film, and specialty applications, among others.
However, free-radical polymerization methods do not allow for the precise control of important polymer properties such as branching, tacticity, molecular weight and molecular weight distribution. For this reason, it is desirable to develop transition metal catalysts capable of carrying out the direct copolymerization of olefins with polar comonomers. Market opportunities and advantages for substantially linear functional polyolefins and other controlled structures are expected in areas such as recreational materials (golf ball covers), durable goods, packaging, adhesives, and alloys.
To date, few systems for the direct copolymerization of olefins and polar comonomers exist. Cationic Pd diimine initiators, developed by Brookhart/DuPont, are capable of producing polyethylenes with up to ˜20 mol % incorporation of acrylate comonomer. However, these materials are very heavily branched, and the acrylate comonomer is overwhelmingly placed at the ends of branches rather than in the main chain (WO 96/23010; J. Am. Chem. Soc. 1996, 118, 267; J. Am. Chem. Soc. 1998, 120, 888). Modified versions of these Pd diimines, and related P—O ligated Pd complexes (developed by Drent), can give more linear copolymers but at the expense of greatly reducing comonomer incorporation (<2 mol %) (WO 2001/92342; Polym. Mat. Sci. Eng. 2002, 86, 319; Polym. Mat. Sci. Eng. 2002, 86, 322; Chem. Commun. 2002, 744; Organometallics 2002, 21, 2836). To date, the most versatile copolymerization catalysts reported are Grubbs' single-component imine-phenoxide “neutral nickel” initiators. These salicylaldimine-ligated complexes can produce relatively linear copolymers of ethylene with functionalized long-chain and norbornene comonomers, having polar incorporations of up to ˜30 mol %.
Recently, ExxonMobil developed a proprietary single-component neutral nickel olefin polymerization catalyst having o-aryl-disubstituted azo-phenoxide ligands (U.S. Ser. No. 10/436,741, filed May 13, 2003). This initiator can produce higher molecular weight polyethylenes and ethylene-octene copolymers than the related imine-phenoxide nickel initiators of Grubbs (which are reported to catalyze copolymerization of olefins with certain polar comonomers). Herein we report a process for the direct copolymerization of ethylene (or other olefins) with functionalized comonomers using our novel catalyst compounds. This catalyst shows certain advantages over the imine-phenoxide nickel initiators, including greater retention of catalyst activity and molecular weight in the presence of functional groups, and greater copolymer linearity or polar comonomer incorporation under certain conditions.
Additional references of interest involving ethylene/polar comonomer copolymerizations include: U.S. Pat. No. 6,410,664; U.S. Pat. No. 6,143,857; U.S. Pat. No. 6,562,922; Ittel, S. D. et al., Chem. Rev. 2000, 100, 1169; Gibson, V. C. et al., Chem. Rev. 2003, 103, 283; DD 99556 (East German patent); U.S. Pat. No. 6,506,704, WO 00/56785; U.S. Pat. No. 6,197,715; U.S. Pat. No. 6,197,714; Stibrany, R. T. et al., Macromolecules 2003, 36, 8584; WO 99/30822; U.S. Pat. No. 6,037,297; U.S. Pat. No. 6,417,303; U.S. Pat. No. 6,180,788; Stibrany, R. T. et al., Polymeric Materials: Science & Engineering 2002, 86, 325; and Stibrany, R. T. et al., in Beyond Metallocenes: Next-Generation Polymerization Catalysts; Patil, A. O.; Hlatky, G. G., Eds.; ACS Symposium Series 857; American Chemical Society: Washington, D.C., 2003, 222.